Dr. Lederberg became interested in exobiology -- the study of life beyond Earth -- in the 1950s, as interest in exploring space began to build in the United States and other countries. He was one of the first scientists to express concern that spacecraft from Earth might carry microbes that could contaminate the moon or other landing sites. He co-chaired the 1964 Summer Study, sponsored by NASA and the Space Studies Board of the National Academy of Science, which outlined the rationale for searching for life on Mars and started to make the search for life beyond Earth intellectually respectable.

He was consulted frequently by NASA during the development of the Viking mission, which carried experiments designed to determine whether life could exist on Mars.

"Joshua Lederberg was one of the guiding lights behind the Viking search for life on Mars and a very close friend and trusted adviser to Jerry Soffen, Viking project scientist" said Langley Research Center senior research scientist Dr. Joel S. Levine. "Lederberg.visited Langley often and was influential in promoting the importance of searching for life outside Earth -- even before that concept was fashionable."

Lederberg has remained active with NASA in the 21st century. In 2000, Baruch Blumberg, then the director of the NASA Astrobiology Institute and a Nobel Laureate himself, included Lederberg on his "Director's Science Council," which consisted of 10 members, most of which were Nobel Laureates with expertise ranging from physics to molecular biology.